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Showing papers on "Acoustic interferometer published in 1996"


Journal ArticleDOI
TL;DR: In this paper, an extension of the ultrasonic spectropy technique was used to determine dispersion of longitudinal waves in a solid at frequencies ranging from 2.2 to 7.6 MHz.
Abstract: The ultrasonic spectroscopy (broadband pulse) technique was applied to simultaneously measure phase velocity and attenuation coefficient of shear waves in a solid at frequencies ranging from 2.2 to 7.6 MHz. This technique is an extension of the ultrasonic spectropy technique currently used in determining dispersion of longitudinal waves.

121 citations


Journal ArticleDOI
01 Nov 1996-EPL
TL;DR: Martinez-Sala et al. as discussed by the authors used the plane-wave method in order to get the band structure of waves propagating in an infinite periodic system and employed, for the first time for acoustic waves, the transfer matrix method to find the transmission coefficient of waves along a system with a finite thickness.
Abstract: We study acoustic waves propagating in two-dimensional (2D) systems consisting of steel cylinders surrounded by air. We use the plane-wave method in order to get the band structure of waves propagating in an infinite periodic system. In addition, we employed, for the first time for acoustic waves, the transfer matrix method in order to find the transmission coefficient of waves propagating along a system with a finite thickness. Both methods are in good agreement with each other and their results agree with recent measurements in a similar system (R. Martinez-Sala et al., Nature, 378 (1995) 241). We also find the optimum conditions for the appearance of spectral gaps.

121 citations


Journal ArticleDOI
TL;DR: The LCPDI is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction.
Abstract: A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. Afocus shift was measured with the LCPDI, and the results are compared with theoretical results.

68 citations


Patent
12 Mar 1996
TL;DR: In this paper, an absolute measurement is determined by a simple mathematical relationship between the measured wavelength and phase changes, where the phase change of the interference signal is continually detected during the wavelength modulation process.
Abstract: An absolute measuring interferometer having a measuring interferometer, a tunable laser emitting a laser beam and a control interferometer for adjusting the air wavelength of the laser beam. The control interferometer adjusts the air wavelength of the laser beam to a specific wavelength value at the ends of each measuring cycle. The wavelength of the tunable laser is continually tuned within the specific wavelength interval where the phase change of the interference signal is continually detected during the wavelength modulation process. An absolute measurement is determined by a simple mathematical relationship between the measured wavelength and phase changes.

58 citations


Journal ArticleDOI
TL;DR: In this article, the stiffness tensor coefficients of anisotropic materials are recovered by scanning a symmetry plane, and four coefficients of the tensor are then recovered with good reliability.
Abstract: A scanned point source‐point receiver technique, based on laser generation and detection of acoustic waves, is used to measure the stiffness coefficients of anisotropic materials. The striking effects that anisotropy gives rise to are analyzed and, when possible, advantage is taken of them. The processing developed for recovering the coefficients is presented and applied starting with simulated or experimental signals. A silicon crystal, for which acoustic wave focusing induced by anisotropy is critically sensitive, is first studied. To provide an accurate interpretation of these waves, the two‐dimensional problem considering a line source is discussed, before analyzing the point source generation. Secondly, a manufactured composite material is characterized by means of this noncontact technique. By scanning a symmetry plane, four coefficients of the stiffness tensor are then recovered with good reliability.

44 citations


Journal ArticleDOI
TL;DR: The refractive-index modulation generated in optical fibers by electrostriction-induced acoustic waves is investigated directly by a pump-probe measurement technique in a 1-km-long fiber Sagnac-loop interferometer as a measure of the acoustic interaction.
Abstract: The refractive-index modulation generated in optical fibers by electrostriction-induced acoustic waves is investigated directly by a pump-probe measurement technique in a 1-km-long fiber Sagnac-loop interferometer. Pump pulses propagating unidirectionally around the loop generate transverse acoustic waves that produce a time-dependent relative phase shift for the probe pulses. The consequent interferometer transmission changes are used as a measure of the acoustic interaction. The acoustic impulse response function of the fiber is measured by use of short optical pulses with a 1-MHz repetition rate. The response consists of a series of peaks separated by ~21 ns with a maximum value of refractive-index modulation of −1.1 × 10−11 generated by the 230-pJ pump pulses. At a higher pulse repetition rate of 100 MHz additional temporal structure is generated in the 0–5-ns period after the pump pulse, leading to a response similar to that observed in long-range soliton interaction.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two reference beam double-pulsed holographic interferometry.
Abstract: The transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two‐reference‐beam double‐pulsed holographic interferometry. The acoustic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itself. A subsequent phase‐stepping procedure is used for quantitative evaluation of the registered two‐dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the free end of the plate, where sound waves propagate into the air in oblique directions from the plate. At the region right above the free end no acoustic waves are observed. Supersonic flexural waves in the plates generate trace‐matched acoustic waves in the surrounding air. Calculations of the corresponding two‐dimensional transient acoustic fields are performed. Those are based on an analytical solution of the Kirchhoff plate equation. Calculated results reproduce the character of the observed transient acoustic waves quite well.

26 citations



Journal ArticleDOI
TL;DR: The phase-stepping technique is demonstrated with a three-step algorithm to measure out-of-plane strain on a f lat metal plate with wavelength modulation of the optical source.
Abstract: Phase stepping by wavelength modulation of the optical source is demonstrated in a path-length unbalanced shearing interferometer. A magnification difference, which accompanies the path-length imbalance in the interferometer, introduces an unwanted radial shear, which is shown to be compensated by inclusion of a block of high-refractive-index material in the longer interferometer arm. The block also increases the phase shift obtained for a given wavelength change. The phase-stepping technique is demonstrated with a three-step algorithm to measure out-of-plane strain on a flat metal plate.

22 citations


Patent
24 Oct 1996
TL;DR: In this article, focused acoustic waves are applied to a patient via a coupling surface, where a number of coupling devices are selectively coupled to the source and a volume equaliser is provided for the acoustic broadening medium.
Abstract: The acoustic therapy device includes a source (1) of focused acoustic waves. A number of coupling devices are selectively coupled to the source. Acoustic waves are applied to a patient via a coupling surface. Each coupling device has a volume such that acoustic waves are conducted freely from a radiation surface to the coupling surfaces. At least one of the coupling devices includes an acoustic broadening medium. At least one coupling device is elastically bendable. A volume equaliser (14) is provided for the acoustic broadening medium.

15 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a sing-around technique employing a fixed path acoustic interferometer operated at a frequency of 2 MHz to estimate the ultrasonic speeds in the liquid phase of 1,1, 1,2-tetrafluoroethane.
Abstract: Ultrasonic speeds in the liquid phase of 1,1,1,2-tetrafluoroethane (CF{sub 3}CH{sub 2}F) have been measured from 243.11 K to 333.15 K and from near the saturation line to about 30 MPa. The measurements were made using a sing-around technique employing a fixed path acoustic interferometer operated at a frequency of 2 MHz. The probable uncertainty in the results was no greater than {+-}0.2% except in the low-density region at near the saturation line at higher temperatures. The vapor pressures have also been observed to within {+-}10 kPa by monitoring the acoustic signal at vapor-liquid equilibrium. When these results were combined, the ultrasonic speeds for the saturated liquid were estimated to within {+-}1 m/s.

Journal ArticleDOI
TL;DR: In this paper, velocity measurements of bulk and Rayleigh waves in a highly anisotropic natural medium (slate) were performed using a standard ultrasonic pulse transmission setup, and the elastic behavior of a block of slate whose faces are traversed by these surface waves was studied, and verified that this rock shows a good fit to a physical model of a solid with an axis of symmetry of revolution.
Abstract: This paper describes experimental results on velocity measurements of bulk and Rayleigh waves in a highly anisotropic natural medium (slate). Bulk waves velocities are measured using a standard ultrasonic pulse transmission setup. The Rayleigh waves are excited using the wedge technique and recorded by an interferometer which detects both the in‐plane and out‐of‐plane components of the displacement they produce in a point of a sample surface. The experiments constitute part of a study of the propagation of surface seismic waves in anisotropic geological structures using scaled‐down models. The elastic behavior of a block of slate whose faces are traversed by these surface waves is studied, and it is verified that this rock shows a good fit to a physical model of a solid with an axis of symmetry of revolution.

Journal ArticleDOI
TL;DR: In this paper, an existing method, based on laser speckle interferometry, was adapted to record the three components of transient vibration induced by an ultrasonic wave at a point on the surface of a solid model.
Abstract: The generation and detection of elastic waves by photoelastic methods, called ‘‘laser ultrasonics,’’ is now a rather commonly used method in research. The aim of this paper is to adapt an existing method, based on laser speckle interferometry, in order to record the three components of transient vibration induced by an ultrasonic wave at a point on the surface of a solid model. A detailed description of the method is given. The reliability of the method is experimentally demonstrated. As an illustration, maps of the local three‐dimensional transient vibration and of the particle trajectories of different points at the surface of a solid are reported.

Journal ArticleDOI
TL;DR: In this paper, the modulational dynamics of a small amplitude, high frequency dispersive wavetrain coupled to acoustic waves is addressed in the framework of the Zakharov-Rubenchik equations.

Journal ArticleDOI
TL;DR: In the case when the beam diameter exceeds the coherence length of the acoustic wave, the fourth-order correlation function is found to contain an interference structure, whereas the intensity angular distribution has a one-peak shape.
Abstract: Angular distributions of the intensity and the fourth-order correlation function are studied for light scattered by acoustic waves with thermal statistics. In the case when the beam diameter exceeds the coherence length of the acoustic wave, the fourth-order correlation function is found to contain an interference structure, whereas the intensity angular distribution has a one-peak shape. \textcopyright{} 1996 The American Physical Society.

Proceedings ArticleDOI
03 Nov 1996
TL;DR: In this paper, the authors used line-focus transducers to image surface acoustic wave propagation based on wave-vector, rather than group-velocity, direction, and applied these techniques to carbon-fiber/epoxy composite materials.
Abstract: Acoustic wavefront imaging using point-focus immersion transducers has enabled us to observe propagation of acoustic waves in anisotropic solids. This technique has been useful for studying both bulk-wave and surface-wave propagation in a variety of materials. By using line-focus transducers, we can image surface acoustic wave propagation based on wave-vector, rather than group-velocity, direction. In this paper we apply these techniques to carbon-fiber/epoxy composite materials.

Journal ArticleDOI
TL;DR: In this article, an optical heterodyne interferometer was developed to enable noncontact detection of ultrasonic motions parallel and perpendicular to the specimen surface, and two optical setups, one for the parallel direction and another for the perpendicular direction, were included in the interferometers.
Abstract: An optical heterodyne interferometer was developed to enable noncontact detection of ultrasonic motions parallel and perpendicular to the specimen surface. Two optical setups, one for the parallel direction and another for the perpendicular direction, were included in the interferometer. The interferometer enabled simultaneous ultrasonic detection in both directions at the same point on the specimen surface without changing the optical layout of the interferometer. For verification of the technique, longitudinal and shear ultrasonic waves generated by piezoelectric transducers were detected by the interferometer.

Journal ArticleDOI
TL;DR: In this article, the incompressibility of the medium was taken into account to lead to nonlinear coupling between acoustic and orientation waves in a nematic liquid crystal, and the regime of nonlinear excitation of orientation wave in the course of propagation of a powerful high frequency acoustic wave in a liquid crystal was investigated.
Abstract: Taking incompressibility of the medium into account is shown to lead to nonlinear coupling between acoustic and orientation waves in a nematic liquid crystal. Equations for three-wave resonant interaction are derived and the regime of nonlinear excitation of orientation waves in the course of propagation of a powerful high frequency acoustic wave in a liquid crystal is investigated.

Journal ArticleDOI
TL;DR: Stroboscopic holographic interferometry has been developed at an advanced undergraduate level allowing real-time imaging of standing sound waves in gas filled, closed tube resonators as mentioned in this paper, and a heterodyne Mach-Zehnder interferometer was first built by students to show the feasibility of interferometric detection of sound wave in a small cell.
Abstract: Stroboscopic holographic interferometry has been developed at an advanced undergraduate level allowing real‐time imaging of standing sound waves in gas filled, closed tube resonators. A heterodyne Mach–Zehnder interferometer was first built by students to show the feasibility of interferometric detection of sound waves in a small cell. In the subsequent holographic study, the laser irradiance is modulated by an acousto‐optic cell at frequencies near that of the standing wave, and a video camera records the fringe motion due to sound pressure changes. Fractional fringe shifts are observed for an air filled cell, and multiple fringe shifts are imaged for the case of freon. Sound reflections from the cell ends are easily observed, with nonsinusoidal waveforms dominating at high intensities due to superposition of resonator harmonics.

Journal ArticleDOI
TL;DR: In this paper, a phase grating was formed with variations in thickness and refractive index with a period of half the wavelength of surface acoustic waves, when a thin film was deposited on a substrate in which a standing surface wave was excited.
Abstract: It was found for the first time that a phase grating was formed with variations in thickness and refractive index with a period of half the wavelength of surface acoustic waves, when a thin film was deposited on a substrate in which a standing surface wave was excited. No such phenomenon has been reported before, and its application to optical elements is expected to be a new application of surface acoustic waves.

Journal ArticleDOI
TL;DR: In this paper, the signal from a point source of ultrasound is detected as a function of space and time, revealing the acoustic wavefront (or group-velocity surface) striking a surface of the solid.
Abstract: We have developed new imaging methods for the study of ultrasonic waves in solids. The signal from a point source of ultrasound is detected as a function of space and time, revealing the acoustic wavefront (or group-velocity surface) striking a surface of the solid. By Fourier transforming the x-y-t “data cube” resulting from a short pulse on silicon, the internal diffraction of acoustic waves is observed.

Proceedings ArticleDOI
03 Nov 1996
TL;DR: A good agreement has been found between the predictions and the acoustic microscope measurements in this article, where the anomalous behavior of the attenuation around the cutoff has been focused on the acoustic wave measurements.
Abstract: The standard surface pre-treatment used on aluminium adherends in aerospace applications produces a porous oxide structure on the adherend surface. The adhesive penetrates some distance into the pores to form a microcomposite. The thickness of these interlayers in a typical aluminium-epoxy joint is of the order of 1 /spl mu/m only. Surface acoustic wave measurements have been carried out with an acoustic microscope at frequencies between 220 and 980 MHz for different thicknesses of oxide layer. A good agreement has been found between the predictions and the acoustic microscope measurements. Attention has been focused on the anomalous behaviour of the attenuation around the cutoff.

Journal ArticleDOI
TL;DR: In this paper, the stability of acoustic waves in a medium moving with a time-variable velocity was analyzed and an instability criterion for these waves was obtained and analyzed for the weak modulation of medium velocity.
Abstract: We analyze the stability of acoustic waves in a medium moving with a time-variable velocity. An instability criterion for these waves is obtained and analyzed for the weak modulation of medium velocity. The harmonics that emerge during the propagation under parametric resonance are shown to have an additional frequency shift.

Book ChapterDOI
17 Apr 1996
TL;DR: In this paper, a multilayer model for the ocean bottom is assumed and the data consist of reflection coefficient measurements (magnitude and phase) in the sea water for obliquely incident acoustic waves.
Abstract: A new algorithm for the reconstruction of the two basic acoustic parameters of the sea floor (density and sound speed) is presented in this communication. A multilayer model for the ocean bottom is assumed and the data consist of reflection coefficient measurements (magnitude and phase) in the sea water for obliquely incident acoustic waves. Since the reconstruction of the two unknown parameters mentioned above is sought, an empirical formula between them must be used in the reconstruction algorithm. The algorithm is based on the use of a recursive formula for the local reflection coefficient above each interface of the sea bottom model. Finally, accurate reconstruction results, based on synthetically obtained reflection data, are obtained.

19 Mar 1996
TL;DR: In this article, the transmission of impulsive acoustic signals into a homogeneous soil medium was investigated using a piezoelectric driver and a hydrophone as the acoustic sources.
Abstract: : The transmission of impulsive acoustic signals into a homogeneous soil medium was investigated. Measurements performed using a piezoelectric driver and a hydrophone as the acoustic sources demonstrate that both types of transmitters (positioned at the air soil interface) are capable of producing acoustic waves in soil. The relative strength of the acoustic signals produced by each source was found to be approximately equal. The angular distribution of acoustic energy transmitted into the soil was found to be omnidirectional. Accelerometers buried within a 1.2 m deep soil box were used to measure the attenuation of acoustic signals as a function of frequency. The attenuation was observed to increase with increasing frequency from a value of approximately 8 dB/ft at 1 kHz to 35 dB/ft at 8 kHz. Measurements of the wave motion at the air soil interface induced by a surface mounted transmitter show that large amplitude surface waves are produced by both types of transmitters. The amplitudes of the observed surface waves were large in comparison to the estimated amplitude of signals produced by subsurface scattering of acoustic waves. A longitudinal wave receiver designed to reduce the amplitude of surface waves in favor of acoustic waves scattered from subsurface targets was successfully tested.